1. Field of the Invention
The invention relates to radiation-sensitive and acid-cleavable compounds and to a radiation-sensitive mixture which is positive-working, i.e., which becomes soluble as a result of irradiation, which contains these compounds. The mixture contains
(a) a binder which is insoluble in water and soluble or at least swellable in aqueous alkaline solutions, and PA1 (b) an oligomeric compound which generates a strong acid under the action of actinic radiation and which has at least one acid-clearable C--O--C bond. PA1 R.sup.2 is a hydrogen atom, an alkyl, alkenyl or aryl radical or the group (R.sup.1 --SO.sub.2 --O--).sub.n X--, PA1 R.sup.3 is a cycloalkylenedialkyl, cycloalkenylenedialkyl, arylenedialkyl, heteroarylenedialkyl, alkylene, alkenylene, alkynylene, cycloalkylene or arylene group, PA1 X is an alkylene, cycloalkylene or arylene group if n is 1, or a (n+1)--valent radical of an alkene, cycloalkene, or arene if n is 2 or 3. PA1 Y is O, S, CO, CO--O, SO.sub.2, SO.sub.2 --O, NR.sup.4, CO--NH, O--CO--NR.sup.5, NH--CO--NR.sup.5 or NR.sup.5 --CO--O, PA1 Z is O, CO--NR.sup.6, O--CO--NR.sup.6 or NH--CO--NR.sup.6, PA1 R.sup.4 is an acyl radical, PA1 R.sup.5 is a hydrogen atom or an alkyl, cycloalkyl, alkenyl, alkynyl or aryl radical, PA1 R.sup.6 is an alkyl, cycloalkyl, alkenyl, alkynyl or aryl radical, PA1 k is an integer from 0, 1, 2, 3 or 4, PA1 m is an integer greater than 1 and n is an integer from 1, 2 or 3,
The invention also relates to a radiation-sensitive recording material produced from this mixture which is suitable for producing photoresists, electronic components, printing plates or for chemical milling.
2. Description of Related Art
The continuing reduction in the size of the structures, for example, in chip manufacture down into the range of less than 1 .mu.m, requires modified lithographic techniques. To form images of such fine structures, radiation of a short wavelength is used, such as high-energy LrV light, electron beams and X-rays. The radiation-sensitive mixture must be adapted to the short-wave radiation. A compilation of the requirements to be met by the radiation-sensitive mixture is given in the article by C. G. Willson "Organic Resist Materials--Theory and Chemistry" [Introduction to Microlithography, Theory, Materials, and Processing, editors L. F. Thompson, C. G. Willson, M. J. Bowden, ACS Symp. Ser., 219, 87 (1983), American Chemical Society, Washington].
There is therefore an increased demand for radiation-sensitive mixtures which can be used in the more recent technologies, such as mid-UV or deep-UV lithography [exposure, for example, with excimer lasers at wave-lengths of 305 nm (XeF), 248 nm (KrF), 193 nm (ArF)], electron beam lithography or X-ray lithography, and which, furthermore, are preferably sensitive in a wide spectral range and correspondingly can also be used in conventional UV lithography.
Positive-working radiation-sensitive mixtures for producing radiation-sensitive recording materials are known. Mixtures which contain o-quinone--diazide derivatives in binders soluble in aqueous alkaline media, for example novolaks or polyhydroxystyrenes, are commercially available. However, the sensitivity of these materials to actinic radiation, and especially high-energy short-wave radiation, such as light from a KrF-excimer laser having a wavelength of 248 nm or electron beams, is inadequate.
Positive-working radiation-sensitive mixtures are also known in which an acid is generated by the action of actinic radiation on a photoinitiator contained in this mixture and this acid then, in a subsequent reaction, renders an acid-cleavable compound likewise contained in the mixture soluble in the irradiated areas under the action of an appropriate, preferably aqueous alkaline developer. Such materials are in general distinguished by an enhanced sensitivity to actinic radiation.
Numerous mixtures are known which contain, as the essential components, a polymeric binder soluble in aqueous alkaline solutions, a solubility-inhibiting compound and a compound which, on irradiation, generates the acid required for cleavage. The binder is in most cases a novolak resin. Many of these mixtures have a high sensitivity to actinic radiation. They are designated as chemically amplified, photocatalytic 3-component systems.
Of these mixtures, those whose acid-clearable component contains one or more acetal units have gained commercial importance. These mixtures have, however, certain disadvantages. They possess only a limited stability on the substrate materials to which they have to be applied, which leads to an unsatisfactory, not reducible reproduction of the image original. This can be improved only by introducing additional protective layers, for example according to DE-A 3,621,376, equivalent to U.S. Pat. No. 4,840,867. The causes of the deterioration in the image reproduction are not fully known and have not been adequately investigated. For example, the process window, i.e., the processing latitude, for the exposure of these mixtures is very narrow and frequently not unambiguously reproducible. In particular, the quality of the image reproduction greatly depends on the time difference between exposure and development, the so-called delay time. In principle, it must be assumed that diffusion processes which cause this behavior are not easily controllable. In addition, however, it may be presumed that, during drying of the mixture on a substrate material, partial vaporization of the photoinitiator or of the acid-unstable compound or segregation of the individual mixture constituents takes place, which is observed with particular frequency in the case of acid-unstable compounds having a low solubility in the usual coating solvents.
It is also known from the papers by C. C. Petropoulos [J. Polym. Sci., Polym. Chem. Ed., 15, 1637 (1977)] that aromatic acetals which carry a nitro group in the vicinal position, are photodecomposable by high-energy UV radiation without acid catalysis, and can be used in positive-working radiation-sensitive recording materials. The photosensitivity of these compounds is likewise inadequate for applications in practice, since their photoreaction cannot be chemically amplified.
In DE-A 3,721,741, equivalent to U.S. Pat. No. 4,883,740, radiation-sensitive mixtures are described which contain a polymeric binder insoluble in water and soluble in aqueous alkaline solutions, and an organic compound which contains at least one acid-cleavable grouping and a grouping which generates a strong acid under the action of radiation. The radiation-sensitive groups described are exclusively onium salt groups, in particular sulfonium salt groups.
The use of onium salts, such as diazonium, phosphonium, sulfonium and iodonium salts, of nonnucleophilic acids such as HSbF.sub.6, HAsF.sub.6 or HPF.sub.6 as photolytic acid generators involves disadvantages which drastically restrict their possible uses in various fields of application. For example, many of the onium salts are toxic. Their solubility is inadequate in many solvents, which is why only a few solvents are suitable for preparing a coating solution. Furthermore, when the onium salts are used, undesired foreign atoms are sometimes introduced which can cause interference with the process, especially in microlithography. Moreover, the onium salts form Bronstedt acids, which have a very severe corrosive action, in the photolysis. These acids attack sensitive substrates, so that the use of such mixtures leads to unsatisfactory results. Halogen compounds such as trichloromethyltriazine derivatives or trichloromethyloxadiazole derivatives also form hydrohalic acids which have a severely corrosive action.
In more recent papers by F. M. Houlihan et al., SPIE 920, 67 (1988), it was shown by reference to positive-working systems that, in addition to the above-mentioned acid generators, nitrobenzyl tosylates, which on exposure generate sulfonic acids having a low migration tendency, can be used in certain acid-unstable resist formulations. It can be deduced from these results that such compounds can also be used for photo-curable systems. However, the sensitivities thus achieved, especially to UV radiation from 350 to 450 nm, and the thermal stability of the photoresists have proven to be inadequate.
Because of the inadequacies and disadvantages described above, there is a demand for radiation-sensitive mixtures which do not have these disadvantages and possess a reactivity suitable in practice.